The most common type of metal container used in the beer and beverage industry is what is commonly referred to as a two-piece can. The two-piece can consists of a first piece comprising a cylindrical can body portion having one end closed with an integral end wall and where, after the filling process, a separately-formed end panel is attached to the upper end of the container by what is referred to as a double seaming process. With the cylindrical body portion, the double seaming process results in the seam extending beyond the peripheral surface of the container body. In such cases, it has been customary in recent years to produce a necked-in portion on the container body adjacent the open end so that the double seam between the container body and the end panel is located within the confines of the periphery of the cylindrical container body. This provides a more compact package for the containers, which in turn lowers the total shipping and storage costs.
Because of the increased demand for this necked-in type of container, considerable efforts have been devoted to produce an apparatus which is capable of reducing the neck and the peripheral edge on a container body in a rapid and reliable manner.
As the cost of materials has increased, it has been found desirable to reduce the amount of material to a minimum, yet preserve the integrity of the container. One area where manufacturers have explored the possibility of reducing the amount of metal used for producing a finished packaging container is a reduction in the wall thickness of the sidewall of the container. Continuous efforts have been directed towards reducing the thickness of the initial blank that is drawn and ironed in the finished container which also reduces the wall thickness of the cylindrical portion of the container during the drawing and ironing process. Whereas it has been possible to reduce the sidewall thickness in the can body to the order of 0.004 inches, the ends remain the normal thickness of 0.012 to 0.013 inches for beer and beverage containers.
This reduction in metal thickness of the body has resulted in inherent problems in producing a necked-in container utilizing the conventional annular necking die where the container is essentially forced into the annular die to reduce the open end of the container or necked-in portion of the open end of the container. This is particularly true where the containers are processed on high-speed equipment.
Various apparatus have been proposed for producing drawn and ironed containers having either a single neck-in portion, a double necked-in portion or possibly even a triple necked-in portion. Examples of such proposals are disclosed in U.S. Pat. Nos. 3,812,696; 3,687,098; 3,983,729; and 4,070,888.
Because of the reduced wall thickness, additional problems have become inherent in reforming the container body during the necking process. Various proposals have been suggested and one of such proposals is to utilized pressurized fluid internally of the container to strengthen the column load force of the sidewall of the container during the necking process. There are particular problems inherent in processes as the speed of production is increased.